There are three modes for Internet Protocol (Internet Protocol, IP for short) address allocation of an access device. In the first mode, a Dynamic Host Configuration Protocol (Dynamic Host Configuration Protocol, DHCP for short) server (server) built in a Broadband Remote Access Server (Broadband Remote Access Server, BRAS for short) allocates IP addressees, wherein an IP address management function, etc., are further built in the BRAS. In the second mode, a DHCP server external to a BRAS allocates an IP address, while the BRAS plays a role of a DHCP relay and maintains users' address renewing information, so as to release control and forward resources of the access device in the case that a user releases an address initiatively or does not renew the address. In the third mode, a Remote Authentication Dial In User Service (Remote Authentication Dial In User Service, RADIUS for short) server authorizes an IP address, and the BRAS need not to have an address management function. At present, in most cases, three modes that a DHCP server is built in a BRAS allocates an IP address, a DHCP server external to a BRAS allocates an IP address and a Remote Authentication Dial In User Service (Remote Authentication Dial In User Service, RADIUS for short) authorize an IP address for a private consumer are mainly adopted.
FIG. 1 is a schematic diagram illustrating a network structure of a dual-host hot backup deployment scene in the prior art in the case that a DHCP server built in a BRAS allocates an IP address, and the network structure mainly includes: a first BRAS 11, a second BRAS 12, a first Digital Subscriber Line Access Multiplexer (Digital Subscriber Line Access Multiplexer, DSLAM for short) 15, a second DSLAM 16, a first Convergent switch (Switch) 13, a second Switch 14 and a Core Router (Core Router, CR for short) 17. The state of the first BRAS 11 is a master state (Master), and the state of the second BRAS is a slave state (Slave). And, both the first BRAS 11 and the second BRAS 12 have a built-in DHCP server. For example, the first BRAS 11 has an address segment 1.1.1.0/24, and the second BRAS 12 has an address segment 2.2.2.0/24. When the first BRAS 11 works normally, if there are 100 users to be online at the first DSLAM 15 side, 100 IP addresses of 1.1.1.0/24 segment are allocated from the first BRAS 11. When failure occurs in a node of the first BRAS 11, the state of the second BRAS 12 is changed from a slave state into a master state, thus enabling the second BRAS 12 to allocate an IP address from 2.2.2.0/24 segment for new users to be online at the first DSLAM 15 side.
The inventor has found at least the following problem in the prior art when realizing the present invention: in a dual-device hot backup scene, when failure occurs in a first BRAS, an IP address is allocated by a second BRAS, thus causing that other IP address(es) in 1.1.1.0/24 segment of the first BRAS cannot be used.